1. Field of the Invention
The present invention relates to wet motor fuel pumps and, more particularly, to wet motor fuel pumps of the type having inlet housings and pump elements that must be precisely aligned.
2. Description of the Prior Art
Prior art wet motor pumps imvolve a large number of precision parts requiring precise alignment, assembly, and operation with each other. With such prior art wet motor pumps, the inlet end and outlet end of the motor shafts are precisely positioned in the respective inlet housing and outlet housing so that the shaft axis is precisely fixed. Such precision shaft positioning is required to prevent the armature windings from interferring with peripheral structure, such as the port plates, the magnets, and even when such precise shaft positioning ample tolerances are provided to account for wear.
Such constraints are compounded in a gerotor pump because of the extremely small clearances that must be perpetually maintained between the tips of the mating gears with respect to each other and to the perimeter of the pumping cavity as well as the sides of each of the gears relative to both axial sides of the pumping cavity. Any degration of the tip clearance or side parallelism reduces the efficiency of the pump.
Another element reducing the efficiency of the pump and increasing the noise generated thereby is the conventional drive arrangement between the motor and the driven gear of the pump. Such drive couplings have heretofore been of the slot and key arrangement type requiring not only that the shaft be precisely aligned with the bore of the driven gear, but also that the key and slot coupling the two are of similar precision. The wear in the slot and key arrangement not only is a known primary failure mode, but also compounds the wear degradation in teeth clearance and parallelism. Accordingly, fuel pumps of the gerotor type are normally comparatively expensive due to the additional precision required therein. Moreover, to provide th requisite precision, the gerotor parts are usually made independently and aligned separately from the inlet housing.